The present invention relates to an apparatus for transferring objects, and more particularly to multiple independent robot assemblies for the simultaneous and independent manipulation of multiple objects, such as semiconductor wafers.
The use of robot arms is a well established manufacturing expedient in applications where human handling is inefficient and/or undesired. For example, in the semiconductor arts robot arms are used to handle wafers during various process steps. Such process steps include those which occur in a reaction chamber, e.g. etching, deposition, passivation, etc., where a sealed environment must be maintained to limit the likelihood of contamination and to ensure that various specific processing conditions are provided.
Current practice includes the use of robot arms to load semiconductor wafers from a loading port into various processing ports within a multiple process chamber system. The robot arms are then employed to retrieve the wafer from a particular port after processing within an associated process chamber. The wafer is then shuttled by the robot arms to a next port for additional processing. When all processing of the wafer within the system is complete, the robot arm returns the semiconductor wafer to the loading port and a next wafer is placed into the system by the robot arm for processing. Typically, a stack of several semiconductor wafers is handled in this manner during each process run, and several wafers are passing through the system simultaneously.
In multiple chamber process systems, it is desirable to have more than one semiconductor wafer in process at a time. In this way, the process system is used to obtain maximum throughput. A typical wafer handling sequence to switch wafers in a process chamber is to remove a wafer from a process chamber, store the wafer in a selected location, pick a new wafer from a storage location, and then place the new wafer in the process chamber. Although this improves use of the system and provides improved throughput, the robot arm itself must go through significant repetitive motion to simply exchange wafers.
To increase the efficiency of robot handling of wafers, a robot arm having the ability to handle two wafers at the same time may be provided. Thus, some equipment manufacturers have provided a robot in which two carrier arms are located at opposed ends of a support, and the support is rotated about a pivot. In this way, one wafer may be stored on one arm while the other arm is used to retrieve and place a second wafer. The arms are then rotated and the stored wafer may be placed as desired. Such a mechanism does not allow the two arms to be present in the same process chamber at the same time, nor does it allow for the immediate replacement of a fresh wafer in a process chamber after a processed wafer is removed, because the support must be rotated 180.degree. to place the wafer on the second arm in a position for loading into the location from which the first wafer was removed. Likewise, simultaneous use of the two arms for placement or removal of wafers from process or storage positions is not possible with this configuration.
Another robot configuration includes a central hub having two opposed arms, each arm arranged for rotation relative to the hub while arcuately fixed in relation to one another. A blade is linked to the free ends of the arms, and a drive is provided for rotating the arms in opposite directions from each other to extend the blade radially from the central hub, and in the same direction to effect a circular movement of the blade about the central hub. Preferably, a second pair of arms extend opposed from the first pair, on the ends of which is connected a second blade. Opposed rotation of the arms in one direction extends the first arm while retracting the second arm. Opposed rotation of the arms in the opposite direction results in retraction of the first arm and extension of the second arm. Simultaneous motion of the arms in the same direction swings the blades in a circular or orbital path around the hub. The use of two blades increases throughput. However, this device still does not permit simultaneous insertion of a fresh wafer into a process chamber as a processed wafer is being withdrawn from the same chamber, or independent use of the blades to simultaneous load into wafers, unload from, wafers or move a wafer between one or more chambers while a second wafer is being loaded or unloaded.